From 0437caa59728387508e58d0a6d95b03c84f2ff1e Mon Sep 17 00:00:00 2001
From: uku <hi@uku.moe>
Date: Mon, 2 Dec 2024 21:14:09 +0100
Subject: [PATCH] feat(day2): init

---
 src/solutions/day_02.rs | 85 +++++++++++++++++++++++++++++++++++++++++
 src/solutions/mod.rs    |  3 +-
 2 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 src/solutions/day_02.rs

diff --git a/src/solutions/day_02.rs b/src/solutions/day_02.rs
new file mode 100644
index 0000000..ac2507c
--- /dev/null
+++ b/src/solutions/day_02.rs
@@ -0,0 +1,85 @@
+use itertools::Itertools;
+
+use crate::common::{Answer, Solution};
+
+pub struct Day02;
+
+impl Solution for Day02 {
+    fn name(&self) -> &'static str {
+        ""
+    }
+
+    fn part_a(&self, input: &str) -> Answer {
+        let reports = input
+            .lines()
+            .filter(|l| {
+                let nums = l.split_whitespace().map(|n| n.parse::<i32>().unwrap());
+
+                is_valid(&nums)
+            })
+            .count();
+
+        Answer::Number(reports as u64)
+    }
+
+    fn part_b(&self, input: &str) -> Answer {
+        let reports = input
+            .lines()
+            .filter(|l| {
+                let nums = l.split_whitespace().map(|n| n.parse::<i32>().unwrap());
+                let valid = is_valid(&nums);
+
+                if !valid {
+                    let len = nums.clone().count();
+                    for skip_i in 0..len {
+                        let new_nums = nums
+                            .clone()
+                            .enumerate()
+                            .filter_map(|(i, n)| (skip_i != i).then_some(n));
+
+                        if is_valid(&new_nums) {
+                            return true;
+                        }
+                    }
+                }
+
+                valid
+            })
+            .count();
+
+        Answer::Number(reports as u64)
+    }
+}
+
+fn is_valid<T: Iterator<Item = i32> + Clone>(nums: &T) -> bool {
+    let diffs = nums.clone().tuple_windows().map(|(a, b)| a - b);
+
+    diffs.clone().all(|d| (-3..=-1).contains(&d)) || diffs.clone().all(|d| (1..=3).contains(&d))
+}
+
+#[cfg(test)]
+mod test {
+    use super::Day02;
+    use crate::common::Solution;
+
+    use indoc::indoc;
+
+    const INPUT: &str = indoc! {"
+        7 6 4 2 1
+        1 2 7 8 9
+        9 7 6 2 1
+        1 3 2 4 5
+        8 6 4 4 1
+        1 3 6 7 9
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(Day02.part_a(INPUT), 2.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(Day02.part_b(INPUT), 4.into());
+    }
+}
diff --git a/src/solutions/mod.rs b/src/solutions/mod.rs
index ded8423..3bc6a6a 100644
--- a/src/solutions/mod.rs
+++ b/src/solutions/mod.rs
@@ -1,5 +1,6 @@
 use crate::common::Solution;
 
 mod day_01;
+mod day_02;
 
-pub const SOLUTIONS: &[&dyn Solution] = &[&day_01::Day01];
+pub const SOLUTIONS: &[&dyn Solution] = &[&day_01::Day01, &day_02::Day02];